Ioannis Varvaris (2013), Nonlinear storage models of unconfined flow through a shallow aquifer on an inclined base and their quasi-steady flow application, MSc Thesis, CUT, CyprusAbstract.Hillslope processes involving flow through an inclined shallow aquifer range from subsurface stormflow to stream base flow (drought flow, or groundwater recession flow). In the case of recharge, the infiltrating water moves vertically as unsaturated flow until it reaches the saturated groundwater, where the flow is approximately parallel to the base of the aquifer. Boussinesq (1901) used the Dupuit-Forchheimer (D-F) hydraulic theory to formulate unconfined groundwater flow through a soil layer resting on an impervious inclined bed, deriving a nonlinear equation for the flow rate that consists of a linear gravity-driven component and a quadratic pressure-gradient component. Inserting that flow rate equation into the differential storage balance equation (volume conservation) Boussinesq obtained a nonlinear second-order partial differential equation for the depth. So far however, only few special solutions have been advanced for that governing equation. The nonlinearity of the equation of Boussinesq is the major obstacle to deriving a general analytical solution for the depth profile of unconfined flow on a sloping base with recharge (from which the discharges could be then determined). Henderson and Wooding (1964) were able to obtain an exact analytical solution for steady unconfined flow on a sloping base, with recharge, and their work deserves special note in the realm of solutions of the nonlinear equation of Boussinesq. However, the absence of a general solution for the transient case, which is of practical interest to hydrologists, has been the motivation for developing approximate solutions of the non-linear equation of Boussinesq. In this work, we derive the aquifer storage function by integrating analytically over the aquifer base the depth profiles resulting from the complete nonlinear Boussinesq equation for steady flow. This storage function consists of a linear and a nonlinear outflow-dependent term. Then, we use this physics-based storage function in the transient storage balance over the hillslope, obtaining analytical solutions of the outflow and the storage, for recharge and drainage, via a quasi-steady flow calculation. The hydraulically derived storage model is thus embedded in a quasi-steady approximation of transient unconfined flow in sloping aquifers. We generalise this hydrologic model of groundwater flow by modifying the storage function to be the weighted sum of the linear and the nonlinear storage terms, determining the weighting factor objectively from a known integral quantity of the flow (either an initial volume of water stored in the aquifer or a drained water volume). We demonstrate the validity of this model through comparisons with experimental data and simulation results.

Zambela Pittaki (2013), Application and Testing of Weibull Distribution in Wind Measurements at Cyprus, Thesis, CUT, CyprusAbstract.The last 5 years considerable effort has been done in encouraging investment on wind energy plans in Cyprus. Two wind farms work already on an operational basis and thoughts for further intrusion of the wind energy in the electric power production of the island exist. This study aims to contribute to the understanding of the available wind power in Cyprus, focusing into the characteristics of the wind flow at two coastal stations, located at Limassol and at Polis Chrysochous. Firstly, a statistical analysis of wind speed and direction data for the selected meteorological stations at the Cyprus coast is carried out. Daily, monthly and annual variations of wind speed are established. The analysis recovers two characteristic periods with roughly uniform well separated patterns, due to the strong influence of sea-breeze. In both stations strong modification of the wind direction exists between the daytime and nighttime hours, when the wind direction almost reverses, (from S to N for Polis and from N to SW for Limassol) reflecting the sea-breeze influence. At the same time, the wind speed exhibits also a profound modification resulting in lower speeds during the night, although this is less evident at Polis Chrysochous, due to the probable existence of katabatic flows. In terms of the Weibull representative distributions of the wind speed data, the fitting of the measured wind speed distributions to the theoretical curves is examined through the application of four different statistical methods, namely: maximum likelihood method, method of moments, power density method and the much less established method of the shape estimation. The application is performed on a 12-hour basis for every month, following the characteristic daily variation of the wind pattern over the island. All the methods are almost equally well performed in terms of well-established independent statistical tests (Kolmogorov-Smirnov, Anderson-Darling and x2) although, as it was expected, the maximum likelihood method proved the most significant. Impressively, however, the last method of the shape estimation is of much more practical interest since it gives the more accurate estimation in terms of the wind power generated from a real wind. This is due to the fact that the efficiency factor of a wind power generator is not constant but depends strongly on the wind speed, especially at the lower range, which is usually the case for Cyprus.

Kiriacos Theodoulides (2014), A conceptual quasi - steady model for sea - aquifer interaction , Thesis, CUT, CyprusAbstract.This thesis analyzes the flow of seawater in a horizontal aquifer with semi-permanent state of flow and conditional pumping. In particular a mathematical model was created in order to calculate the evolution of the location of marine wedge inside the aquifer when subjected changing pumping conditions. The model was applied to the Akrotiri aquifer in Cyprus and different scenarios of pumping fluctuations were examined. To calculate the position in which seawater enters the aquifer Ghyben and Herzberg, in late 1800, derived the first equation (Ghyben-Herzberg) describing the interaction of salt with fresh water by calculating the position of the wedge caused due to ingress of seawater relating the shape and position of the interface with the hydrological parameters of the aquifer. The assumptions of Ghyben-Herzberg theory were the main obstacle to resolving the detailed evolution of the profile of fresh and seawater and thus the calculation of the position in which the marine wedge is inside the aquifer. The main disadvantage is the assumption is that the interface of saltwater and freshwater is immovable while actually moving toward the interior of the aquifer. Generally there were several assumptions and theories for understanding the behavior of ingress seawater in underground aquifers, with the most important assumption of Strack (1976) who introduced the concept of a single potential that represents the two zones of fresh and saltwater, to require solving only one equation that is valid for both. To create this single equation, Dupuit assumption is adopted for the case of flow of fresh water and the relationship of Ghyben-Herzberg is also used to determine the depth of the interface. All previous studies and theories about the behavior of aquifers utilized the steady state of the flow. The present study is based on the assumption of a sharp interface of Strack and Dupuit-Forchheimer making use of the equations to build a prototype quasi-steady state flow model in order to calculate the position of marine wedge and maximum allowable pumping rate to avoid the destroy of the aquifer. The model was applied to the Akrotiri aquifer in Cyprus and tested with previous results with success. It is expected to become a useful tool in the future for modeling the behaviour of groundwater aquifers.

Niki Katzi (2014), DNS of linearly forced isotropic turbulence, Thesis, CUT, CyprusAbstract.In this Thesis we investigated in general the turbulent flow and its characteristics in the overall context and we focused, in particular, to the case of homogeneous isotropic turbulence. DNS, are the numerical solution of the basic equations of fluid dynamics (Navier-Stokes), using powerful computers till now they have been proven to be a valuable tool for the study of the turbulence. We performed direct numerical simulations (DNS) using linear forcing of isotropic turbulence, in order to investigate the statistical stationarity that is produced by applying this method in the spectral space. Furthermore, we compared our results with past results of Rosales and Meneveau (2005). The results were very similar and in almost perfect agreement. Furthermore, we solved analytically the Pao’s energy transfer model in spectral space for linearly forced isotropic turbulence. The results of the statistical stationarity were compared against the results from direct numerical simulations. In the range of the available Reynolds numbers that we studied, the model was accurate and revealed the key characteristics of the generated isotropic turbulence.